Drug & supplement interaction

Melatonin + 6-Mercaptopurine

6-Mercaptopurine brand name: Purinethol.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Melatonin has a moderate interaction with 6-Mercaptopurine. Theoretically, melatonin might interfere with immunosuppressive therapy.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Melatonin and 6-Mercaptopurine

Here is the interaction we found between these two, with the evidence behind it.

Moderate

IMMUNOSUPPRESSANTS

Why this applies to 6-Mercaptopurine

6-Mercaptopurine falls under IMMUNOSUPPRESSANTS — the group Melatonin interacts with.

Theoretically, melatonin might interfere with immunosuppressive therapy.
Melatonin can stimulate immune function. Theoretically, melatonin might interfere with immunosuppressive therapy.
Severity Moderate Likelihood Possible Evidence B

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the idea behind this pairing. Melatonin can gently nudge your immune system to be a little more active. 6-Mercaptopurine (Purinethol) works in the opposite direction, calming down or suppressing immune and white blood cell activity to fight leukemia. So in theory, melatonin could push back against what your medication is trying to do, possibly making it work a touch less effectively.

I want to be honest with you though: this concern is mostly theoretical and based on weaker evidence, so we don't actually know how much it matters in real life. Because mercaptopurine is a serious chemotherapy drug, please don't start melatonin on your own. Run it by your oncologist or pharmacist first so they can weigh in for your specific situation.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Lissoni P, Barni S, Mandala M, et al. Decreased toxicity and increased efficacy of cancer chemotherapy using the pineal hormone melatonin in metastatic solic tumor patients with poor clinical status. Eur J Cancer 1999;35:1688-92.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Melatonin Also Interacts With Other Medications

Melatonin has 1,115 moderate, 345 minor known drug interactions in our database — the 6-Mercaptopurine one above is one of them. If you take anything else, check it against the full list below.

Moderate 1,115 Minor 345 No known interaction 1,370 (incl. 6-Mercaptopurine)
Taking anything else?

Check Another of Your Medications Against Melatonin

Covers the 2,830 medications we’ve checked against Melatonin. Pick one to open its full report.

From our Q&A

Questions About Melatonin or 6-Mercaptopurine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Melatonin or 6-Mercaptopurine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With 6-Mercaptopurine

This page covers Melatonin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the 6-Mercaptopurine page lists 106 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Active Hexose Correlated Compound (ahcc) (moderate).

By severity: 4 major · 92 moderate · 10 minor.

From our pharmacist’s overview on the 6-Mercaptopurine page

“6-Mercaptopurine (Purinethol) works by dialing down your immune system, whether for leukemia or inflammatory bowel disease, and that makes this a list to check with real care. The four major-rated entries come first.”

Reviewed by 2 · Jul 18, 2026

Open the 6-Mercaptopurine interaction page

One more smart check

Taking Melatonin as Part of a Dietary Supplement Product? Check It for Interactions

We hold 2,885 real supplement products containing Melatonin, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Melatonin. Your product may carry other ingredients that interact with 6-Mercaptopurine too, on top of Melatonin — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Melatonin and 6-Mercaptopurine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Melatonin
Top 5%

#54 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication 6-Mercaptopurine
Steady interest

#1,649 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Melatonin

What is Melatonin?

Melatonin
  • Trouble falling asleep (insomnia)
  • Jet lag
  • Delayed sleep phase syndrome
  • Non-24-hour sleep-wake disorder
  • Shift-work sleep problems
  • Sleep problems in some children with conditions like autism or ADHD

Melatonin is a hormone your body makes naturally to help control your sleep-wake cycle, and the supplement form is widely used to help with sleep timing problems and jet lag. The evidence is strongest for certain circadian (body-clock) disorders and is more mixed for everyday insomnia. It is generally well tolerated for short-term use, but talk with your pharmacist or doctor before starting, especially for children or during pregnancy.

Read the full Melatonin monograph & all interactions
Medication

About Mercaptopurine

What Is Mercaptopurine Used For?

Brand name: Purinethol

Mercaptopurine — available as a tablet and as an oral suspension — is used to treat acute lymphoblastic leukemia (ALL), a type of blood cancer. It is given as part of a combination chemotherapy maintenance regimen, meaning it works alongside other cancer medicines to keep leukemia in remission.

Both the tablet form and the oral suspension form carry this indication for adult and pediatric patients. The oral suspension is particularly useful for patients who cannot swallow tablets.

See full Mercaptopurine drug information
Keep checking

Other Drugs & Melatonin

Browse every other medication we’ve checked against Melatonin — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
1,115Moderate
345Minor
1,369No known interaction
1,115 Moderate 345 Minor 1,369 No interaction
Moderate

1,115 interactions

Showing 60 of 1,115 moderate interactions — see all 1,115 on the Melatonin page.

Minor

345 interactions

Showing 60 of 345 minor interactions — see all 345 on the Melatonin page.

No interaction 1,369 drugs checked — show the list

We also checked Melatonin against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,369 medications checked with no known interaction — see the full Melatonin list.

See the full Melatonin interactions page
See every supplement checked against 6-Mercaptopurine, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Melatonin monograph › Uses, safety, and every drug interaction in one place 6-Mercaptopurine supplement interactions › Every supplement checked against 6-Mercaptopurine, ranked by severity Mercaptopurine drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Melatonin and 6-Mercaptopurine Together: Common Questions

Can you take Melatonin with 6-Mercaptopurine?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Melatonin and 6-Mercaptopurine interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About 6-Mercaptopurine and Melatonin?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.